The use of copper alloys as wiring material substitutes for conventional aluminum alloys is advancing, with the aim of increasing the performance of LSI devices. Aluminum alloy wirings have been subjected to micromachining primarily by dry etching methods, but the same methods are poorly suitable for application to copper alloy wirings.
The “damascene method” has therefore been largely employed for micromachining of copper alloy wirings, in which method a thin-film of a copper alloy is accumulated and embedded on an insulating film having pre-formed furrows, and the copper alloy thin-film on sections other than the furrows is removed by CMP to form embedded wiring (see Patent document 1).
The common method of CMP for metals such as copper alloys involves attaching an abrasive pad onto a circular polishing plate (platen), dipping the abrasive pad surface into a polishing agent for metals, pressing the metal film-formed surface of a substrate against it, rotating the polishing platen with a prescribed pressure (hereunder referred to as “polishing pressure”) being applied from the back side, and removing the metal film on the heights by mechanical friction between the polishing agent and the heights of the metal film.
The polishing agent used for CMP usually comprises an oxidizing agent and an abrasive, with further addition of a metal oxide solubilizer or protective film-forming agent as necessary.
In CMP employing such a polishing agent, presumably the metal film surface is first oxidized by the oxidizing agent and the oxidation layer is shaved by the abrasive, resulting in polishing of the metal film. Here, since the oxidation layer on the metal surface in the recesses does not significantly contact with the abrasive pad and is not reached by the shaving effect of the abrasive, the metal layer on the heights is removed as CMP proceeds, thus flattening the substrate surface (see Non-patent document 1, for example).
When the damascene method is applied for common manufacturing of an LSI, the film thickness of the copper alloy used is about 1 μm (1000 nm), and a polishing agent with a polishing speed of about 0.5 μm/min (500 nm/min) is used (see Patent document 2, for example).
In recent years, however, CMP treatment of copper is being applied for manufacture of high performance microcircuit boards such as package boards, and also in the formation of Through Silicon Vias (TSV) that have become an object of interest in new mounting methods. TSVs, however, require polishing of metals (copper alloys) with film thicknesses of 5 μm and greater, and sometimes 10 μm and greater, and therefore the polishing speeds achieved with conventional LSI polishing agents are inadequate, and polishing agents that allow polishing at higher polishing speeds are desired.
Patent document 3 thus discloses a polishing agent which allows polishing of copper alloy films at polishing speeds that are higher than the prior art (about 2.2-2.9 μm/min).